Posttraumatic Stress Disorder (PTSD) is defined by characteristic symptoms that develop following exposure to a distressing event that involves actual or threatened death or serious injury, or a threat to the physical integrity of self or others (DSM-IV; American Psychiatric Association; 1994). Included in the symptoms of PTSD are disturbances in attention, such as increased arousal, difficulty concentrating, hypervigilance, exaggerated startle response, and heightened physiological reactivity to cues that symbolize or resemble the event. Despite the high prevalence and morbidity of PTSD (Browne & Finkelhor, 1986), comparatively little research has been conducted to advance the understanding of the neurocognitive aspects of this disorder. As pointed out by Charney, et al. (1994), the dearth of neurocognitive research on PTSD contrasts sharply with the large body of investigations of the behavioral, biochemical, and neurophysiological effects of stress in laboratory animals. These animal studies support the notion that neural mechanisms and neurochemical alterations contribute to the etiology and/or the persistence of symptoms associated with PTSD. In this regard, PTSD provides a unique and valuable model of the protracted effects of a traumatic event on human neurobiology and cognition. Based on theoretical issues pertaining to the neurobiological and behavioral symptoms of PTSD, and the neurobiology of attention, the present study is proposed to investigate the neurocognitive aspects of attention in PTSD using both neuropsychological and electrophysiological measures. The subjects will include a sample of Vietnam combat veterans with PTSD, Vietnam combat veterans without PTSD, and civilian controls. Event- related potentials will be obtained using a continuous performance test paradigm under conditions of sustained and focused attention. Neuropsychological measures of attention, memory, and executive functions also will be obtained. The behavioral and electrophysiological measures will provide information about the possible role of disturbances in anterior and posterior attentional systems in the development and maintenance of PTSD symptomatology.